System of railway signaling and train control



Ma'rch 6, 1928. 1,662,047 J. A. MILLER SYSTEM OF RAILWAY SIGNALING- AND'TRAIN @IONTROL o l Filed June 25 1920 3 Sheets-Sheet 1 1,662,047 J. A. MILLER SYSTEM OF RAILWAY SIGNALING AND TRAINCONTROL Original Filed June 25; 1920 3 Sheets-Shee. 2

March 6, I928.

. g 185. &. \NAMJ Patented Mar. 5, 1928.

cnrrsn s'rA'r s' PATENT oFFi-c J'UHN a. inrnnnn, or ennn'nsnn; on-nironnm, nssrenon; BY Mnsn'n ASSIGNMENTS;

r Union sWIToH & sreivnn or swrssvnnn, r'ENNsY'L ANIA, A 003- EQit'tATIOli' O PENNSYLVANIA.

SYSTEM OF RAILVFAY SIGHALING AND TRAIN CONTROL.

Application filed June 25, 1920, Serial The object of this invention is to provide a system of railway signaling and train contro double track electric railways.

i, :qiolicable to either single track or My 1nven tion contemplates and provides certain combinations of apparatus and circuits whereby high frequency alternating currents are em ployed for the purpose of controllingboth road-way and train-carried signals to afford appropriate indications t r a oi conditions caution and danger tor the guidof the motorn'ien in charge of the ins operating on the railways aforesaid.

My invention furthermi'ire contemplates the provision, in combination withthe traincarried signals, of means for causing the sounding or" an audible signal and the applicat our

ion of the brakes prior to the entry of the or train, equipped with the improvements of my invention, into an occupied lilo of i application brakes if, in the first instance, the motor- ;i releases the brakes and proceeds declr, and for causin a-second spite the danger indication.

Other ob ects and advantages of the systen 1 shown and described herein-will appear as the following detailed description progresses. i

In the accompanying drawings,

Figure l is a diagrammatic representation fit] a trollcywire or third rail of an electric lway, said trolley wire or third rail being divided into block sections and suitably coni'icctoii for cooperation with the signaling cqidpmcnt of my invention. i

figure 2 .is a diagrannnatic representation my invention applied'to one track of a doi'ible track railway, wherein signals are employed on the movable units, and

i 'ure 3 is a similar vlew illustratingmy e non as it maybe employed in a railded as being a trolley wire or third rail rate we with the running rails of an electric railway. This trolley Wire or third rail as the case may be, is divided into block tions A. B, C, D, E and F by insulation No. 391,7eo. Renewed July is, 1927.,

joints Insulation joints 2 are bridged by choke coils 0 propulsion cu ductor l, but

which permit the passage of rrent impressed upon the conenectively prevent the passage of the high frequency signaling currents presently to be mentioned;

"I have not deemed it necessary to illustrate the means for impressing propulsion current upon arrangements known in the 'the conductor .1, as suitable tor this purpose are well art to, which my invention relates. Each. insulation joint 2 is furthermore bridged instance two) by flplurality (in the present Ji 'x' T) Oi by-passes i each icy-pass being adjusted with regard to its capacity and inductance to permit the passage of a high frequency current of a definite frequency and to preclude the passage of currents oil diilerent frequencies.

For convenience I provided eachreference letter P with a SilbSOIlPh'lllCllCtttlIlg the particular rrequency which the corresponding by-pass is adjusted to Reference letters pass. y

G indicate generators of high frequency current, each of said generators arranged toiinpress a current of a dell nite frequency upon one of the blocks of the conductor 1, Condensers 0 7 through transformer T. are included in the circults of the transformer secondaries to prevent the propulslon current 'irom being short-cirouited to gro laries, f

und through the transformer The sources of high "frequency current G may be of any approved and welln'nown type, and i'or that reason have been indlcated in'the accon'ipanylng drawings by circles.

For convenience, reference letter Ur with a subscript indicating have provided each the particular frequency which its connected generator intended to'ii'npress upon the block-section oi the conductor 1 with which said generator is associated. In thesystein l, l, employ generators delivering frequencies of 5.000, 8,000 and 10,000. In

Figure 1, the

direction of travel is indicated by an arrow and it is to be understood that impress a de upon a block tar end.

Under opcr each of the generators isso connected asto finite high frequency current of conductor 1 at its GXltl or ating conditions, generators G are continuously in operation. For the moment disregarding the presence of a car in any block, it will be seen that by virtue of i the tuning of the several by-passes P and the factthat I employ generators of the three diil'erent frequencies noted on the drawings, each block of theconductor l is normally excited with high frequency currents of three different frequencies. In other words, each block section of conductor 1 is normally excited with the *high frequency current impressed thereon by its associated high frequency generator G1 andby' v rtue of the tuned by-passes P is excited with the high frequency current delivered by the high frequency generator of the nextblock in advance and is furthermorecexcited with the high frequency current delivered 'by the high frequency current generator associated with the second block iniadvance thereof.

Adjacent the ends of the blocks of conductor 1 are way-side signals consisting ofthe signal poles b, each of which is provided with visual signals which maybe in the form of green," yellow andred lamps indicated by reference lettersG, Y and B, respectively. Energization of any one of the green lamps, of course, indicates that the motor-man may proceed'past that lamp and. into the next block' with entire safety. The energization of a yellow lamp indicates that he may proceed but slowly and withcaution, and the encrgization of the red lamp indicates that it is dangerous to proceed. The several lamps of each pole S derive their energizing current from a common battery i and are controlled by the armatures 5 and 6 of relays It and R The circuit connections of theseveral lamps are such that when both 'armatures 5 and 6 are attracted or, in other words, lie against their respective front contacts, the green (safety) lamp is lighted, when'the armature 5 lies against its back contact and the armature 6 is attracted, the yellow (caution) lamp is lighted, and when armature 6 lies against its back contact the red (danger) lamp is lighted.

Relays R andR in each instance are connected with high frequency detectors of the three-element vacuum-valve type, the detectors connected with relays R emg designated V and the detectors connected with relays It being designated V The proper elements of detectors V and V are in each instance connected with the secondaries of transformers TR. The primary of each of the transformers TR has one end thereof grounded and its other end connected to the adjawnt block of the trolley wire or third rail 1 by a conductor in which is interposed a condenser to prevent the propulsion cur rent from being short-circuited to ground through the primarv'of the transformer. It will be noted that the tuning of the transformers TB is of the parallel resonance type.

or in other words, the condensers which are adjusted with respect to the inductance of the several transformer primaries to tune the latter are connected in parallel with the said transformer primaries. I have found that a parallel resonant circuit oll'ersan extremely high impedance to the passage of the current of the frequency to which it is tuned, and in this respect differs radically cuit breaker, and thence through the controller and motor to the rails in the usual manner. Attention is directed to the fact that a choke coil 9 is interposed in conductor 8 to prevent any of the high fre uency current from being short-circuited tirough the n'opulsion circuit. The portions of the carv equipment with which we are most concerned at present are the several transformers TRX, the several primaries of which are tuned in series resonance to frequencies of 5,000, 8,000 and 10,000. One terminal of the primary of each of the transformers TRX is grounded to the car wheels, while the other end is connected to trolley 7 through a connection common to the several transformer primaries in which is interposed a condenser to prevent short-circuiting or the propulsion current through the transformer primaries. It will be noted that the condensers which constitute the capacities by which the transformer primaries are tuned to their respective frequencies are connected in series with the said transformer primaries.

i Preliminary to explaining the operation of the circuits and apparatus of Figure 1, I will briefly refer to certain phenomena which account for the practicability of the present in-.

vention. A conductor, such as a trolley wire, having distributed inductance and capacity, may be tuned to respond to a particu lar frequency that maybe impressed upon it. It has been discoveredthat if two series resonant circuits be connected between such a conductorand the ground, the one of said series resonant circuits nearest the source will absorb practically all of the energy,

leaving little or none of the energy to traverse the series resonant circuit more remote from the source. The trolley 7 and any one of the primaries of transformers TRX of Figure 2, together with its capacity, in series, constitutes FJGI'IGS resonant circuit which, when connected between the trolley wire and no i , i1 l v or the frequency bered that the primaries of the transformers Tlrt associated with the road-wa si nals form parts of parallel resonant circuits, of-

felin coin Jaratively high im Jedance to the a: I, passage of currents of the frequency to which it tuned, while the primaries of.

the movable unit-carried transformers TRX are connected in series resonant circints,

each ofwhich offers a comparatively low impedance to the passage of the current to which it is tuned; It is a fact that in series resonance tuning, when perfect resonance is obtained, the impedance of the circuit is reduced practically to the ohmic resistance of the circuit. It will be understood that theseveral parallel resonant circuits comprising the primaries of the transformers TB- of Figure 1 will absorb but a very small amount of energy. On the other hand, each of the seriesresonant eircuits comprising a primary of one of the transformers TEX of Figure 2 acts as a short-circuit for the particular frequency current to which it is tuned. It is because of these d flering characteristics of parallel resonant circuits and series resonant circuits that it is possible to actuate a road-way signal with but small absorption of energy, and utilize a series resonant circuit on a mow able unit for the purpose of short-circuiting all of the high frequency current for which the series resonant circuit is tuned. V I

Referring now to Figure 1, it will be ob ved that a movable unit M is indicated being located in block D. The relays R and R used in connection with the road-way signal at the entrance to rgized because their respective actuating}: frequencies from generator GSOOO of block C and generator G of block D are cutoff by the series resonance circuits of the movable unit M. Since both relays are de-energized, lamp R at the entrance to block D is fact that the armature of lighted, due to the againstits heel; con

each of said relays lies tact. block D in no way deprives the transformer illlt at the entrance to block E of current of 5000 frequency, but it does deprive the transformer T'R of its current of 10,000 frequency. Consequently, the relay l t at the entrance to block E remains energized while the relay R at the same point is (lo-energized. This relation of the relays results in the energization of the yellow lamp the entrance to block E. This yellow or block D are de-en- The presence of the movable unit M in I caution lamp ofcourse, torman approaching the entranceto block E that he should proceed with caution, because there is amovable unit in block D. 1

As the movable unit M enters block C, high frequency current from generator G' of block D will be restored into blocks D and it. This will result-in the energization of relay R at the entrance to block E, thereby giving a clear indication at theentrance to block E. Relay R at the entrance to block D will also be energized, thereby subsituting a caution indication for the danger indication at the entrance to block D. Simultane ously with this action the signal at the entrance to block C will display a danger indication, because the series resonant circuits of the movable unit M are now absorbing all of the high frequency currentsfrom genera tor G of block B and generator 8000 block C, this of course resulting in the deenergization of relays R and R atthe en-r trance to block C. a

In so i'aras concerns the trolley wire, the insulation joints thereof, the by-pa-ses at the block ends, the roadway signals and appurtenant equipment, the arrangen'ient shown in Figure 2 may be regarded as identical with that of Figure 1. In order to afford room for proper illustration ofthe circuits of the movable unit, it has been necessary in Figure 2 to illustrate the roadway signals and appurtenant equipment by mere symbols. Referring aarticularly to the circuits f the movable unit, which is occupying block F of the trolley wire 1, it-will be noted that the secondaries of the tuned transformers TRX TRX and TRX are connected, with vacuum tube detectors V V and V, which in turn are electrically connected with relays R R and R".

The movable unit shown in block F wnich is receiving high frequency currents from generator (i ofblock F, generator Ga of block E and generator G of block 1), has its relays ll, ll and It closed. Thesethree relays being closed, master relay 85 will he energized, its'circuitbeing closed from battery 56, through lead 55, ari'nature 81 of relay it lead all), armature 26' of relay R lead 42, armature 21 of relay R leads 90 and 88, winding 8521, leads Stand 61, back to battery. Since green signal lamp G is connected in parallel with winding 85A, it isnow lighted to indicate safety. The train line valve X is held closed by solenoid 60, the circuit including hich proceeds from battery 56, throughlead 57, armaturetli', lead 73, the winding and thence through leads 58 and 61 back to battery 563' In a similar manner the whistle valve Z is held closed by the solenoid 59,

indicates to any mos the circuit of which is traced from battery to. battery 56. Safetyconditions are displayed onthe movable unit and the WlliStlG andtrain line valves are held closed solong as the three transformers 'lR TR and TR ofthe movable unit are receiving currents of the frequencies to which they are tuned.

, Assume a movable unit to be located in block 0 as indicated. High frequency current from generator G of block C will be cutoil'drom the anterior portion of block C andentirely from blocks D and E. More over the high tlrequencycurrent from generator (Ji of block ll will becut oil from the anterior portionoi block 0 and entirely fromblock 1). I i y p Assume now thatithe movable unitshown in block F- proceeds into block Since high frequency current otgcnerator G of block (lie no longer present in block E, relay R will be tie-energized, causing the greensignal lampG to be tie-energized. The ma ter relay 85, however, will continue to remain energized from battery 56, through lead 55, armature 32, lead 50, arinature 27, lead eel (relay It being (lo-energized, the armature 27 lies against its back contact), armature 22, loads 91, 8t and 8!), through winding 85B and thence through leads 92, 84 and 61, back to battery 56. Since yellow signal lamp Y is in pa 'allel with winding 8513 the caution indication will now be given. 7

Assume now that the movable unit proeeeds through block E and into block D.

Since high frequency current from generator (i of block B and generator-Gr of block 0 will both be cut oil from block D, relays R and R will be bothde-energized. Master relay 85 will also be ole-energized and yellow signal lamp Y extinguished. Red signal lamp R will then be lighted, its circuit being traced from battery 56, through lead 57, armature (57 (relay R being de-energized), lead 87, through red lamp R and thence through lead 61, back to battery The openingof master relay 85 will lie-energize the train line and whistle valve solenoids 60 and 59, thereby applying the brakes and sounding the Whistle of the movable unit in the usual manner. Sometimes the driver of the movable unit desires to proceed slowlydespite the indication of danger. lease the brakes by closing the train line valve. To close the train line valve, he closes push button 80A which closes the circuit of relay 82 from battery 56, through lead 55, armature 34, lead 93', armature 69, contact 70, lead 78, push button 80A, relay winding 82, leads 83, 8-l and 61, back to the battery 56. When the push button is released, relay S2 isheld closed through its armature 66 and lead 81 which form a bridge around. push button 80A. The train To do this he must reline valve is closed by solenoid Winding 60, the circuit of the latter being traced from battery 55, through lead 55, armature 34, lead 93, armature (39, lead 78, contact 76, armature (Jet, lead 94, the solenoid winding (50 and thence through leads and (31, back to battery 56. The movable unit may now proceed through block l), but only with red light it energized and with the whistle sounding. y

If the movable unit proceeds throu h block Dand enters block C, relay R will also become tie-energized which in turn will tie-energize relay 8; and consequently deenergize the train line valve solenoid (50, thereby causing the brakes to be applied a secondtiine.

b akes, push button 80B may be used to energize relay 82, closing the circuit of saidrelay from the battery 56, through lead 55,

armature lead 54-, arn'iature 30, lead 48, armature 25, lead (52, push button 8013, relay winding 81!, leads d3, 8% and (ll. back to the battery 56. The push button being released, relay 82 is held closed by armature (55 and its cr'intactund lead 81 which bridge the push button 8015. The train line valve soleuoidYiO is energized to release the brakes, as described above, when push button 80A was ClllPiOb'Cdll) energize the relay SQ.

it will be noted that the circuits are so arranged that it requires the receiving ofhigh frequency currents of three frequencies by the detectors of the movable unit to ive a clear or safety indication. The receiving of any two frequencies will give a caution signal, indicating that the second block in advance is occupied, but the reception of but one frequency will give a danger indication, together jwith an application of brakes, and will indicate that the block next in advance is occupied. The absence of all frequencies will give a danger indication and a second brake application. 1

Assume the movable unit, the signal circuit ofiwhich has been just described, to be stationary. As the movable unit in advance thereof moves from block to block. th high frequency currents will be restored in their respective blocks and the movable unit in the rear will receive the proper iiulications, as willbe understood from the previous description. I a

In order to make clear the functions and purposes of the circuits and apparatus of my invention, I have selected certain conditions which actually occur in practice. It is not deemed necessary or desirable in this specification to trace each and every circuit changethat occurs under each and every condition that may occur in practice. The foregoing description is thought to be sulliciently clear to enable anyone skilled in the art readily to follow the functioning oi the circuits and apparatus under every conceivare provided at each end of each block ratherthan merely at one end of each block, as is the case in double track operation. The arrangement of Figure 3 differs from that of Figure 2 in the further respect that bypasses for the additional frequencies are provided aroundthe insulating joints at the block ends.

In Figure 3 the additional high frequency generators are indicated as H 'lmoo and G the subscripts indicating the frequencies delivered bythe several additional generators. Theadditional lay-passes are indicated by reference characters P with suitable subscripts indicating the frequencies to which they are tuned. The additional way-side signal poles are indicated at S and it will be noted that the green, yellow and red lamps of the additional signal poles S are controlled by the high frequency currents of 12,000, 14,000 and 16,000 frequency to govern east-bound traffic in precisely the same manner as the signal lamps of the signal poles S are controlled by the currents of 5,000, 8,000 and 10,000 frequency to govern west-bound traffic.

I contemplate that when my invention is applied to single track operation, each movable unit shall be provided with two sets of detectors, one set to be employed when the movable unit is traveling in one direction and the other set to be used when the movable unit is traveling in the opposite direction. In Figure 3 the additional detectors which would be brought into play when the direction of the west-bound car is changed, are indicated within the square 19, while the corresponding detectors of the east-bound unit are indicated within the square 19'.

I have endeavored to illustrate simplified, rather than complex embodiments of my invention. It will be understood, of course, that in actual practice it may be desirable to have certain detectors more sens1tive than will be possible when the circuit arrangements herein shown are followed in detail. ll hen itis desirablethatthe detectors be very sensitive, the use of an amplifieror a series of amplifiers in connection with any detector will of course, suggest itself to any.- one skilled in the art For this reason, I

have not deemed it necessary to illustrate such amplifying devices. Furthermore, it will be under-stood that in certaincases it will not be'fcasible to have the windings of i connected dire tly in circuitwith the dot ccors, particularly where the relays comprise a plurality of armatures and, therefore, require the application of considerable energy for their operation. "In such cases the use of local circuits controlled by the .de' tectors' will readily suggest itself to those skilled in the art. In this connection I might suggest that the relays B It and R might very well be included in local circuits controlled by the detectors V V and V 1 re I a I wish to have it understood that when,

in the appended claims, I refer to a trolley wire as the conductor through which pro.- pulsion and signaling current is supplied to a movable unit, the words trolley wire? are intended to-cover a third rail or other equivalent means for carrying the currents ,mentioned. a i 7 Having thus described my invention,what I claim as new and desire to secure by Letters Patent of the United States, is:

1. A system of the classdescribedcom: prising in combination witha section of a trolley wire, means for impressing a high frequency current thereon, a road-way signal apparatus comprising a high frequency detector connected with the said trolley wire section and adjusted to respond to the frequency impressed thereon, together with a movable unit provided with an audible signal comprising a high frequency detector electrically connected with the trolley wire section through a series resonant circuit, connection of theseries resonant circuit of the vehicle with the trolley wire-section intermediate the point of application of the high frequency current and the road-way signal apparatus serving to deprive the latter of the high frequency current aforesaid.

2. A system of the class described com prising in combination with a section of a trolley, wire, means for impressing a high frequency current thereon,a road-way signal apparatus comprising a high frequency detector electricallyconnected with the trolley' wire section, and movable unit provided'with signal apparatus comprising a high frequency detector also electrically connected with the trolley wire section, con-. nection of the series resonant circuit of the vehicle with the trolley wire section intermediate the point of application of the high frequency current and the road-way'signal apparatus serving to deprive the latter of the high frequency current aforesaid.

3. A system of the class described com,- prising in combination with a section of a trolley wire, means for impressing a big frequency current thereon, a road-way signal apparatus comprising a high frequency detector electrically connected with thetrol yj Sectioin'and a movable unit pro- 7 vided'with signal apparatus comprising a connected with the trolley wire section, the

said detector being excited from the trolley wire; section through a parallel resonant branch circuit.

5. 111 combination'with a section of a trolley wire and means for impressing a high frequency current thereon, a road-way signal apparatus comprising a high frequency detector permanently electrically connected with said trolley wire section, and a movable unit comprising signal apparatus including a high frequency current detector excited from thetrolley wire section through a series resonant branch circuit, connection of the series resonant circuit of the vehicle with the trolley wire section intermediate tlie'pointof application of the high frequency current and the road-way signal apparatus serving to deprive the latter of the high frequency current aforesaid.

6.1; system of the class described comprising a trolley 'wire divided into block sections, means for impressing a highv fre quency current upon each block section, the high frequency current impressed upon each block section being dili'erent in frequency from the high frequencycurrent impressed upon the block next 'inadvance thereof, tuned by-passesbetweenadjacent block sections whereby each section may receive the high frequency current impressed upon the block section in advance, and a movable unit provided with signaling apparatus comprising a detector adapted to respond to each of the high frequencies employed.

7. A system ofthe class described com prising a trolley wire divided into block sections, means for impressing a high frequency currentupon each block sect-ion, the high frequency current impressed upon each block section being different in. frequency from the high frequency current impressed upon the block nextin advance thereof, tuned by-passes between adjacent block sections whereby each section may receive the high frequency currentimpressed upon the block section in advance, a road-way signal associated with each block section, each road way signal comprising a detector adapted to respond to the high frequency current impressed upon its associated block scctionand also another detector adapted to respond to the high frequency current impressed upon the block section in advance of the section wherewithsaid last mentioned detector is connected. M 1

8. A system of the class described (011% prising a trolley wire divided into block sections, means for=impressing a high fre quency current uponeach block section, the high frequency current impressed upon each block section being dili'erent in frequency from the high frequency current impressed upon the block next in advance thereof, tuned by-passes between adjacent block sections whereby each section may receive the high frequency current impressed upon the block section in advance. a road-way signal associated with each block section, each road-way signal comprising a detector adapted to respond to the high frequency current impressed upon its associated block section and also another detector adapted to rcspond .to the high frequency current impressed upon the block section in advance of the section wherewith said last mentioned detector isconnected, together with a movable unit comprisingsignaling apparatus excited from. whichever block section with whichthe vehicle is connected, said last mentioned signaling apparatus being cxcited through a series resonant circuit.

9. In combination with at least three successive sections of a trolley wire and means for impressing diilcrent high frequency currents on said sections and tuned. lay-passes between contiguous sections whereby one section may partake of the high, frequency ion current impressed upon each of the two sec- 7 tions in advancethereof.

10. In combination with at least three successive sections of a trolley wire and means for impressing different frequency currents on said sections and iuncd hypasses between contiguous sections whereby one section may partake of the high frc quency current impressed upon each of: the two sections in advance thereof, in comhimn tionwith a movable unit comprising signaling apparatus including three high frequency current detectors, each of said dctectors arranged to respond to one of the frequencies employed.

11. In combination with at least three successive sectionsof a trolley wire and means for impressing different frequency currents on Said sectionsand tuncdhy-passes between contiguous sections whereby one section may partake of the high frequency current impressed upon each of the two secllll tionsin advance thereof, together with a movable unit comprising signaling apparatus including three high frequency current detectors, each of said detectors arranged to respond to one of the frequencies employed,

" pressed upon each of the signaling apparatus of the movable unit also comprising means adapted to give indication or safety, danger and caution depending upon the number. and relation of detectors exciton at one time.

in combination with atrolley wire section, means for impressing ahigh frequency current upon one end thereof, and a road-way signal apparatus comprising a high frequency current detector excited from the other end ot the trolley wire section through a parallel i'esonant branch circuit. V

18.111 combination with a trolley wire section, means for impressing a high frequency current upon one end thereof, a roadway signal.apparatus comp-rising a high frequency current detector excited from the other end of the trolley wire section through a parallel resonant b ich circuit, and a movable unit comprising i a series resonant circuit adapted to divert the high frequency current away from the detector of the roadway signal apparatus when said serzes resonant circuit is connected with the trolley wire section between the parallel resonant circuit and the source of high frequency current.

14-. In combination with at least three successive sections of atrolley wire and means for impressing diiierent frequency currents on said sections and tuned lay-passes between contiguous sections whereby one section may partake of the high frequency current imthe two sections in advance thereof, a movable unit comprising signaling apparatus including three high frequency current detectors, each of said detectors arranged to respond to one of the frequencies employed, the signaling apparatus of the movable unit also con'n'irising means adapted to give an indication of safety when the detectors of the movable unit are detecting three trequenoies, an ind cation of caution when the said detectors are detecting two frequencies, and an indication of danger when said detectors are detecting but one frequency or no frequency.

15. A. system of the class described com prising a trolley wire divided into block sections, means for impressing a high frequency current upon each section, the frequency of the currents impressed upon any successive three bloclr sections being different. and tuned bypasses between contiguous sections whereby any section may partake of the high frequency currents impressed upon the two sections in advance thereof.

16. In a system of the class described, the combination with at least three successive block sections of a trolley wire. means for im sing di'tlerent high treouency currents on blocl s?- tions. tuned 1 v-passes connecting contiguous sections whereby one section may partake of the higlri'requency current impressed upon the two'block sec-' tions in advance thereof, choke coils adapted to carrypropulsion current from one section to another, and road-way and movableunit carried signals controlled by said high :tre-' quency currents to afford indications of danger. caution and satety.

17. In combination with a plurality of successive block sections, of a trolley wire and tuned ivy-passes between contiguous sections,,means for impressing high frequency currents of different frequency upon con-' tions, means tor impressing high frequency currents of different frequency upon contiguous block sections, and a wayside signal apparatus associated with each block section comprising a pair of detectors connected with that block section, one of each pair of detectors being responsive to the high treouency current impressed upon its associated block section and the other detector being responsive to the high frequency current impressed upon a contiguous block section, said detectors being excited through parallel resonant branch circuits;

19. In combination with a. plurality of successive block sections, of a trolley wire i and tuned bypasses between contiguous sections, meansfor impressing high frequency currents of different frequency upon contiguous hlock'sections, and a wayside signal apparatus associated with each block section comprising a pair of detectors connected with that block section, one of each pair of detectors being responsive to the high frequency current impressedupon its associated block section, and the other detector being responsive to the highftrequency current impressed upon a contiguous block section,

together with means associated with each wayside signal arranged to indicate danger when both detectors are (lo-energized, caution when but one is energized, and safety when both are energized.

20. A system ofthe class described. comprising in combination with sections of a. trolley wire, means for impressing high frequency currents thereon, and a roadway signal apparatus comprising high frequency detectors connected with said trolley wire sections respectively and ad isted selectively to respond each to definite frequency impressed thereon, together with a movable unit comprising a high frequency detector adapted to-be electrically connected with the trolley wire sections through a series resonant circuit, connection of the series resonant circuit of the vehicle with a trolley wire section intermediate the point of application of the high frequency currents and the roadway signal apparatuses serving-t0 deprivethe latterof the high frequency currents aforesaid. V y

219A system of the. class described comprising a conducting medium dividediinto block sections, means for impressing high frequency currents of different frequencies on each of three; successive block sections, a movable unit arranged to move over said block sections, andsignal controlling deblock sections. s gnal controlling, devices carried by said movable unit responsive to said dill'el'eut frequencies. respectively, and signalscontrolled by said devices for indicatingthe oceupiedor HDOlKfHPlOd condition of a plurality of: succeeding hlo ck sections.

Inwitness whereofil hereunto subscribe my name this 11th day of June. 1920.

JOHN A. MILLER. 

